10-Gbit/s transmission over 300-m standard multimode fiber using multilevel coding and 2-channel WDM

A combination of multilevel coding schemes and simple two-channel wavelength division multiplexing (WDM) at 1300 and 1550 nm was used to transmit an aggregate of 10 Gbit/s over 300 m of multimode fiber that is typical of that employed in current Local Area Networks (LANs). It was shown that this technique could be a simple solution for achieving 10 Gigabit ethernet links over installed multimode fiber building backbones.

High-power and picosecond pulse generation from a passively Q-switched tapered InGaAs/GaAs laser

Tapered waveguides have been used for enhancing pulse powers in Q-switched AlGaAs and InGaAsP lasers. This paper reports on passively Q-switched pulses with 1.53 W peak power and 41-ps FWHM from an InGaAs/GasAs (970 nm) double-contact tapered semiconductor laser in a well defined single-lobed far-field.

Performance of 10 Gbit/s VCSELs operating at 85°C

Oxide-confined VCSELs that are able to operate at modulation speeds of 10 Gbit/s at operating temperatures up to 85°C are demonstrated. This level of performance makes these VCSELs attractive sources for commercial applications in the computer interconnect industry.

High speed reconfiguration of dual-purpose vertical cavity surface emitting laser/detector

High-speed configuration results of a conventional 850 nm VCSEL that is modified to operate as an efficient avalanche detector as well as a laser are discussed. The measured laser-to-detector reconfiguration delay of 3.2 ns is longer than the 1.2 ns detector-to-detector reconfiguration delay.

Single-photon detection using a quantum dot field effect transistor

A novel device for detection of single photons based on a GaAs/AlGaAs modulation doped field effect transistor (MODFET) which does not rely on avalanche processes is proposed. The optimal channel electron densities and quantum dot parameters for detection of single photons are discussed.

2D-lattice distributed reflector laser

A single-contact, mode-hop-free, single longitudinal mode laser operating cw under large signal modulation at 2.5 Gbit/s at room temperature was created by introducing a short etched region around the ridge-waveguide of a Fabry-Perot laser. The device could be suitable for use in extended range data communications applications.

Subcarrier modulation for transmission of 1-Gbit/s channels over 500 m of 62.5-μm multimode fiber

The use of two different subcarriers at frequencies up to 5.5 GHz each transmitting 1 Gbit/s over 500 m of multimode fiber (MMF) is demonstrated. By transmitting the two subcarrier channels simultaneously alongside the baseband signal, an aggregate bit rate of 2.8 Gbit/s is possible.

All-optical switching in a vertical coupler space switch employing photocarrier-induced nonlinearity

A novel compact integrated nonlinear optical switch is demonstrated. Using a high-power picosecond pulse of 5-ps pulsewidth and 250-MHz repetition rate, all-optical switching with a contrast ratio of 23 dB has been achieved using an in-fiber input power < 14 dBm (100 pJ/pulse). The switch speed depends on the carrier sweep-out time, which can be reduced to the 10 ps range by either applying a reverse bias or by introduction of carrier recombination centers in the active layer.

An advanced multi-configuration stator well cooling test facility

Optimisation of cooling systems within gas turbine engines is of great interest to engine manufacturers seeking gains in performance, efficiency and component life. The effectiveness of coolant delivery is governed by complex flows within the stator wells and the interaction of main annulus and cooling air in the vicinity of the rim seals. This paper reports the development of a test facility which allows the interaction of cooling air and main gas paths to be measured at conditions representative of those found in modern gas turbine engines. The test facility features a two stage turbine with an overall pressure ratio of approximately 2.6:1. Hot air is supplied to the main annulus using a Rolls-Royce Dart compressor driven by an aero-derivative engine plant. Cooling air can be delivered to the stator wells at multiple locations and at a range of flow rates which cover bulk ingestion through to bulk egress. The facility has been designed with adaptable geometry to enable rapid changes of cooling air path configuration. The coolant delivery system allows swift and accurate changes to the flow settings such that thermal transients may be performed. Particular attention has been focused on obtaining high accuracy data, using a radio telemetry system, as well as thorough through-calibration practices. Temperature measurements can now be made on both rotating and stationary discs with a long term uncertainty in the region of 0.3 K. A gas concentration measurement system has also been developed to obtain direct measurement of re-ingestion and rim seal exchange flows. High resolution displacement sensors have been installed in order to measure hot running geometry. This paper documents the commissioning of a test facility which is unique in terms of rapid configuration changes, non-dimensional engine matching and the instrumentation density and resolution. Example data for each of the measurement systems is presented. This includes the effect of coolant flow rate on the metal temperatures within the upstream cavity of the turbine stator well, the axial displacement of the rotor assembly during a commissioning test, and the effect of coolant flow rate on mixing in the downstream cavity of the stator well. Copyright © 2010 by ASME.

Hierarchical electrohydrodynamic structures for surface-enhanced Raman scattering (adv. Mater. 23/2012).

On page OP 175, U. Steiner and co-workers destabilise polymer trilayer films using an electric field to generate separated micrometre-sized core-shell pillars, which are further modified by selective polymer dissolution to yield polymer core columns surrounded by a rim and micro-volcano rim structures. When coated with gold and decorated with Raman active probes, all three structure types give rise to substantial enhancement in surface-enhanced Raman scattering (SERS). Since this SERS enhancement arises from each of the isolated structures in the array, these surface patterns are an ideal platform for multiplexed SERS detection.

Adaptive enhancement of multimode fibre bandwidth by twin-spot offset launch

A binary grating on a Spatial Light Modulator generates twin antiphase spots with adjustable positions across the core of a multimode fibre allowing adaptive excitation of antisymmetric mode-groups for improving modal dispersion or modal multiplexing. © 2011 IEEE.

Fibre laser microvia drilling and ablation of Si with tuneable pulse shapes

The dramatic increase in hole quality on single crystalline silicon with an 1 μm fiber laser has been reported recently, it redefines the processing options for Si at that wavelength. This study investigated the effects of the MOPA based pulse tuning on the changes of the machined depth and the mass removal mechanism for the generation of microvia holes. Hole depths were measured and surface morphology studied using SEM and optical interferometric profilometry. The pulse peak power was found to strongly influence the material removal mechanism with fixed pulse duration. High peak powers (>1 kW) gave vaporization dominated ablation, left a limited re solidified molten layer and clean hole formation. The pulse duration was found to strongly influence the machined depth. Longer pulse durations generated deeper holes with constant peak power (>1 kW). In comparison with the DPSS UV laser, the IR fiber laser of longer pulse durations machined deeper holes and generated less resolidifed melt beyond the hole rim at high fluencies. The comparison suggests that some applications (microvia drilling) of the DPSS UV laser can be replaced with the more flexible, low cost IR fiber laser. © KSPE and Springer 2012.

Large Eddy Simulation for Turbines: Methodologies, Cost and Future Outlooks

Flows throughout different zones of turbines have been investigated using large eddy simulation (LES) and hybrid Reynolds-averaged Navier–Stokes-LES (RANS-LES) methods and contrasted with RANS modeling, which is more typically used in the design environment. The studied cases include low and high-pressure turbine cascades, real surface roughness effects, internal cooling ducts, trailing edge cut-backs, and labyrinth and rim seals. Evidence is presented that shows that LES and hybrid RANS-LES produces higher quality data than RANS/URANS for a wide range of flows. The higher level of physics that is resolved allows for greater flow physics insight, which is valuable for improving designs and refining lower order models. Turbine zones are categorized by flow type to assist in choosing the appropriate eddy resolving method and to estimate the computational cost.

Mode-locking using right-angle waveguide, based nanotube saturable absorber

We report passive mode-locking of an Er-doped fiber laser using carbon nanotubes deposited on the facet of a right-angle optical waveguide. © 2013 IEEE.

The absorption of sound by helmholtz resonators with and without flow

Helmholtz resonators are commonly used as absorbers of incident acoustic power. Theoretical and experimental investigations have been performed in the four cases of no mean flow, grazing mean flow, bias mean flow and a combination of grazing and bias mean flows. In the absence of a mean flow, the absorption coefficient (deflned as the proportion of incident energy absorbed) is a non-linear function of the acoustic pressure and high incident acoustic pressures are required before the absorption becomes signiflcant. In contrast, when there is a mean flow present, either grazing or bias, the absorption is linear and thus absorption coefficient is independent of the magnitude of the acoustic pressure, and absorption is obtained over a wider range of frequencies. Non-linear effects are only discernible very close to resonance and at very-high amplitude. With grazing mean flow, there is the undesirable effect that sound can be generated over a range of frequencies due to the interaction between the unsteadily shed vorticity waves and the downstream edge of the aperture. This production is not observed when there is a bias flow because here the vorticity is shed all around the rim of the aperture and swept away by the mean flow. When there is both a grazing mean flow and a mean bias flow, we flnd that only a small amount of bias mean flow, compared with grazing mean flow, is required to destroy the production of acoustic energy. © 2002 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc.